PS 5.2 Solving Average
Speed and Velocity
Problems
The formula v = d/t can be used to
solve speed or velocity problems.
Why?
Using the formula
• In the formula, “v” can represent velocity
or speed.
• “d” can represent distance or
displacement.
• The use of the variable depends on the
context of the problem.
• The term speed or velocity refers to
average speed or average velocity.
Information for calculations.
Things to remember:
• When calculating average speed using v = d/t,
the average speed equals the total distance over
the total time. Ignore the direction.
Remember
• When calculating average velocity using the
same formula, it is the total displacement over
the total time.
Total displacement may be different from total
distance.
o Why?
o
Remember
• When indicating average velocity, a
direction must be given. This will be the
same as the total displacement.
Remember
• The total displacement is the distance and
direction from the starting point.
• If the direction of the motion is changing,
the velocity will not be constant even if the
speed is constant.
Using the formula.
• Always use the GUESS method.
• Calculate the speed of a paper plane that travels
a distance of 19 meters in 5 seconds.
o
Answer: 3.8 m/s
Practice problems
• Calculate the distance a car moves if it has a
speed of 65 miles/hr and travels for 1.5 hours.
o
Answer 97.5 miles.
• How long does it take a toy car with a velocity of
45 cm/s to travel 145 cm?
o
Answer 3.2 seconds
One Last Thing:
• Why is instantaneous velocity at any given
point not the same as the average
velocity?
Think about a car race.
Average velocity is the total displacement
divided by the total time. In a race there are
many starts, stops, turns, and speed changes.
o The speed or velocity at an instant could be a
lot higher than the average.
o
o